``\emph{Recursion} (adjective: \emph{recursive}) occurs when a thing is defined 
in terms of itself or of its type.
\emph{Recursion} is used in a variety of disciplines ranging from linguistics 
to logic.
The most common application of \emph{recursion} is in mathematics and computer 
science,
where a function being defined is applied within its own definition.''

Source and more information: \url{https://en.wikipedia.org/wiki/Recursion}